I updated to UP5.I chose to keep all config filesI installed mint-meta-debian-mate and mint-meta-debian-cinnamon

I have very similar experience. With UP5 suddenly no sound is present. VLC shows a message box saying, that it cannot play audio. No sound icon is present at the bottom right. In cinnamon settings I confirmed that the sound applet is enabled and disabled it and re-enabled just to make sure. The same happens when I log on to my other user where I use MATE/Compiz setup.

I also had numerous other issues (low fps in flash/ cannot logon to cinnamon after logging on to MATE/Compiz, etc.) which forced me to roll back to my Clonezilla backup (UP4). (I love you Clonezilla ).

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I can reproduce the "no sound issue". On another PC I have a VirtualBox on which I installed linuxmint-201204-mate-cinnamon-dvd-64bit.iso. I then updated to UP5. Then I installed mint-meta-debian-cinnamon and mint-meta-debian-mate. I rebooted and no sound on the VM too.

I have sound after a reboot but then I eventually lose it again. All the sound controls show the sound is unmuted, and there are no errors in VLC or flash etc, just no sound. Even when I suspend and hibernate, there are no beeps. It's like the sound is 100% completely disconnected.